Buggy code:
public class TreeItem extends Item { Tree parent ; TreeItem parentItem ; TreeItem [ ] items ; int itemCount ; String [ ] strings ; Image [ ] images ; boolean checked ; boolean grayed ; boolean cached ; Color foreground ; Color background ; Color [ ] cellForeground ; Color [ ] cellBackground ; Font font ; Font [ ] cellFont ; int width = - 1 ; SWTTreeItem handle ; static final int IMAGETEXT_MARGIN = 2 ; public TreeItem ( Tree parent , int style ) { } public TreeItem ( Tree parent , int style , int index ) { } public TreeItem ( TreeItem parentItem , int style ) { } public TreeItem ( TreeItem parentItem , int style , int index ) { } TreeItem ( Tree parent , TreeItem parentItem , int style , int index , boolean create ) { } static TreeItem checkNull ( TreeItem item ) { } static Tree checkNull ( Tree parent ) { } static int checkIndex ( int index ) { } int calculateWidth ( int index , GC gc ) { } protected void checkSubclass ( ) { } void clear ( ) { } public void clear ( int index , boolean all ) { } public void clearAll ( boolean all ) { } void clearSelection ( ) { } NSObject createString ( int index ) { } void deregister ( ) { } void destroyWidget ( ) { } public Color getBackground ( ) { } public Color getBackground ( int index ) { } public Rectangle getBounds ( ) { } public Rectangle getBounds ( int index ) { } public boolean getChecked ( ) { } public boolean getExpanded ( ) { } public Font getFont ( ) { } public Font getFont ( int index ) { } public Color getForeground ( ) { } public Color getForeground ( int index ) { } public boolean getGrayed ( ) { } public Image getImage ( ) { } public Image getImage ( int index ) { } public Rectangle getImageBounds ( int index ) { } public TreeItem getItem ( int index ) { } public int getItemCount ( ) { } public TreeItem [ ] getItems ( ) { } String getNameText ( ) { } public Tree getParent ( ) { } public TreeItem getParentItem ( ) { } public String getText ( ) { } public String getText ( int index ) { } public Rectangle getTextBounds ( int index ) { } public int indexOf ( TreeItem item ) { } void redraw ( int columnIndex ) { } void register ( ) { } void release ( boolean destroy ) { } void releaseChildren ( boolean destroy ) { } void releaseHandle ( ) { } void releaseWidget ( ) { } public void removeAll ( ) { } public void setBackground ( Color color ) { } public void setBackground ( int index , Color color ) { } public void setChecked ( boolean checked ) { } public void setExpanded ( boolean expanded ) { } public void setFont ( Font font ) { } public void setFont ( int index , Font font ) { checkWidget ( ) ; if ( ( font != null ) && ( font . isDisposed ( ) ) ) { SWT . error ( ERROR_INVALID_ARGUMENT ) ; } int count = Math . max ( 1 , parent . columnCount ) ; if ( ( 0 > index ) || ( index > ( count - 1 ) ) ) return ; if ( ( cellFont ) == null ) { if ( font == null ) return ; cellFont = new Font [ count ] ; } <START_BUG> Font oldFont = this . font ; <END_BUG> if ( oldFont == font ) return ; cellFont [ index ] = font ; if ( ( oldFont != null ) && ( oldFont . equals ( font ) ) ) return ; width = - 1 ; cached = true ; redraw ( index ) ; } public void setForeground ( Color color ) { } public void setForeground ( int index , Color color ) { } public void setGrayed ( boolean grayed ) { } public void setImage ( Image [ ] images ) { } public void setImage ( int index , Image image ) { } public void setImage ( Image image ) { } public void setItemCount ( int count ) { } public void setText ( String [ ] strings ) { } public void setText ( int index , String string ) { } public void setText ( String string ) { } }

Fix:
Font oldFont = cellFont [ index ] ;